For each sample, the number, hour, tow direction, wind speed, surface 

 temperature, mean water column temperature (weighted), bottom temperature, 

 water level function, light intensity, tidal factor, inside volume, outside volume, time 

 of first oblique tow, time between tows and time of second oblique tow were 

 recorded. 



SINGLE STATION ANALYSIS 



The expected sources of variability in these data are categorized and summarized 

 as follows: 



Major Source 



Effect on Density Data 



Seasonal 



Time of Day 



Net Differences 



Changes in abundance over the three 

 sampling days 



Changes in abundance over a 24 hour 

 period due to tidal cycle and/ or 

 water temperature, and diurnal cycle 



Differences between the two samples 

 from nets A and B 



Avoidance 



Changes in abundance over a range of 

 tow velocities. Individual species 

 responses may be light dependent 

 as well 



It was found from an analysis of the physical data that mean tow velocities from 

 north and south tows (with or against tidal currents) were significantly different. 

 Therefore it will be necessary to compare overall mean densities from north and 

 south tows. In order to do this it is first necessary to detrend the data by means of a 

 polynomial function, and test for the significance of the residuals from various 

 detrending functions. After detrending the residuals can be used to test for the effect 

 of tow direction alone. 



It should be noted that if a harmonic response to time is demonstrable the 

 response of the system variables to time cannot be effectively measured by means of 

 a linear model. 



The 275 valid observations in the data set can be classified according to certain 

 mean effects as follows: 



N ^(ng) X (n^) -. (Nj^) x. (r) 



m = 275 



342 



